Conventional steering of a wheeled motor vehicle is typically achieved by the vehicle operator (driver) rotating a steering wheel that is arranged in the passenger compartment of the vehicle to turn the steerable road wheels. Conventional steering systems generally include a rack and pinion type steering assembly operatively coupled to the road wheels and a steering column coupled between the steering wheel and the rack and pinion assembly for converting angular rotation of the steering wheel into a sliding motion on the rack to effect steering operation of the road wheels.
In order to reduce the amount of driver effort that is required to rotate the steering wheel conventional steering systems typically include a power assisted force actuator that assists the operator with rotation of the steering wheel to overcome opposing forces such as road load forces on the road wheels and friction forces in the steering assembly. The amount of power assistance generally varies depending on the speed of the vehicle and the amount of effort applied by the driver to the steering wheel. Herein, the term “steering assembly” refers to the mechanical parts of the steering equipment whereas the term “steering system” also includes controlling equipment, if present.
Conventional power steering systems typically employ either hydraulic power assist or electric power assist. In contrast to hydraulic power assist systems, the electric power steering system offers variable assist capabilities, more efficient energy consumption, reduced mechanism complexity, increased reliability, and responsive on-demand steering assist, as well as other advantages.
The electric power steering (EPS) system employs an electric motor for applying a controlled amount of torque to the steering assembly to assist the driver in turning the steering wheel. The conventional electric power steering system is generally configured with a feedback control system that electrically amplifies the driver's steering torque input to the steering system to realize improved steering comfort and performance. The electric power steering system typically includes a rotatable steering wheel, a steering shaft, a rack and pinion assembly, a gear box assembly, and an electric motor.
The torque to the steering assembly includes of the driver's input torque as well as of a feedback torque which is due to external influences such as wheel imbalances, wheel to road interactions, the mechanical parts of the steering assembly or irregularities in the response of the electric motor. Whereas the feedback of the wheel to road interaction to the driver is usually desirable, the other contributions may affect the riding comfort and security. It is therefore advantageous to provide active or passive damping facilities to reduce undesired components of the torque feedback. In particular, a controller for the electric motor may be used for the implementation of an active vibration suppression functionality.